This invention relates generally to semiconductor manufacturing, and more specifically to methods and apparatus for applying an encapsulant to a flip chip.
Typically, in flip chip packaging, one or more integrated circuits (IC) chips are mounted on a substrate to form an electronic substrate. Solder balls (also known as solder bumps), which are mounted on the electrical connection pads of the flip chip are aligned with the corresponding electrical connection pads on the substrate. The flip chip and the substrate are then heated to cause the solder to melt (or xe2x80x9creflowxe2x80x9d) and wet the electrical connection pads of the substrate. The substrate and flip chip are then cooled to solidify the solder thereby forming the desired electrical connections.
As with any IC chip mounted on a substrate surface, differences in the thermal expansion coefficients between the chip and the surface can cause stress and fatigue in these connections as the substrate is subjected to further heat/cool cycles during subsequent processing. A common method of reducing this stress, and providing better adhesion, is to fill the gap between the chip and the mounting surface with a suitable polymeric underfill resin.
Furthermore, IC chips mounted on substrates are frequently coated with a polymeric encapsulation resin to protect the IC chip from outside contamination and mechanical stress. However, separate application of the underfill and the encapsulant requires extra process steps. Additionally, the encapsulant may not be compatible with the underfill.
Known methods which apply the underfill and the encapsulant simultaneously typically require extra steps for masking the electrical contact area of the solder balls or else require etching steps to remove encapsulant from these areas. Therefore, a method for simultaneously underfilling and encapsulating an IC chip without masking or removal steps is desirable.
In one preferred embodiment, the invention is a method for encapsulating and underfilling a lip chip, the method comprising the steps of: providing a flip chip having projections of conductive material on one side of the flip chip, the projections having a proximate end attached to the flip chip and a distal end opposite the proximate end; immersing the flip chip in a polymer bath, wherein the polymer bath covers the flip chip and part of the projections up to a point between the proximate end of the projection and the distal end of the projection; removing the flip chip from the polymer bath such that a coating of polymer adheres to the flip chip and the part of the projections covered by the polymer bath to form a coated flip chip having the distal ends of the projections uncoated; applying ultraviolet light or heat (e.g., IR radiation) to the coated flip chip such that an outer layer of the coating cures to form a skin-cured flip chip; placing the skin-cured flip chip on a substrate board to form an assembly; heating the assembly such that: (i) the conductive material forms an electrical junction between the flip chip and the substrate; (ii) the polymer from the polymer coating on the flip chip underfills and encapsulates the flip chip; and, (iii) the polymer from the coating cures.
In another preferred embodiment, the invention is a method for encapsulating and underfilling a flip chip, the method comprising the steps of: providing a flip chip having projections of conductive material on one side of the flip chip, the projections having a proximate end attached to the flip chip and a distal end opposite the proximate end; providing a pick-up tip, the pick-up tip having indentations corresponding to the projections on the flip chip, wherein the indentations are in fluid communication with a vacuum source; positioning the pick-up tip in contact with, or close proximity to, the flip chip such that the indentations align with and partially cover the projections; applying a vacuum through the indentations such that the flip chip is secured to the pick-up tip; repositioning the pick-up tip such that the flip chip secured to the pick-up tip is immersed in a polymer bath, wherein the polymer bath covers the flip chip and part of the projections up to a point between the proximate end of the projection and the distal end of the projection; removing the flip chip from the polymer bath such that a coating of polymer adheres to the flip chip and the part of the projections covered by the polymer bath to form a coated flip chip having the distal ends of the projections are uncoated; applying ultraviolet light or heat (e.g., IR radiation) to the coated flip chip such that an outer layer of the coating cures to form a skin-cured flip chip; releasing the skin-cured flip chip from the pick-up tip; placing the skin-cured flip chip on a substrate board to form an assembly; heating the assembly such that: (i) the conductive material forms an electrical junction between the flip chip and the substrate; (ii) the polymer from the polymer coating on the flip chip underfills and encapsulates the flip chip; and, (iii) the polymer from the coating cures.
In another preferred embodiment, the invention is a method for encapsulating and underfilling a flip chip, the method comprising the steps of: providing a flip chip having projections of conductive material on one side of the flip chip, the projections having a proximate end attached to the flip chip and a distal end opposite the proximate end; securing the flip chip to a pick-up tip by means of a vacuum; positioning the pick-up tip such that the flip chip attached thereto is partially immersed in a polymer bath to a level between the proximate end and the distal end of the projections; removing the flip chip from the polymer bath such that a coating of the polymer remains in contact with the flip chip such that the distal ends of the projections are uncoated; applying ultraviolet light or heat (e.g., IR radiation) to the coated flip chip such that an outer layer of the coating cures to form a skin-cured flip chip; releasing the skin-cured flip chip from the pick-up tip; placing the skin-cured flip chip on a substrate board to form an assembly; heating the assembly such that: (i) the conductive material forms an electrical junction between the flip chip and the substrate; (ii) the polymer from the polymer coating on the flip chip underfills and encapsulates the flip chip; and, (iii) the polymer from the coating cures.
In another preferred embodiment, the invention is a method for encapsulating and underfilling a flip chip, the method comprising the steps of: providing a flip chip having projections of conductive material on one side of the flip chip, the projections having a proximate end attached to the flip chip and a distal end opposite the proximate end; providing a pick-up tip, the pick-up tip having indentations corresponding to the projections on the flip chip, the indentations in fluid communication with a vacuum source; positioning the pick-up tip in contact with, or close proximity to, the flip chip such that the indentations align with and partially cover the solder balls; applying a vacuum through the indentations such that the flip chip is secured to the pick-up tip; repositioning the pick-up tip such that the flip chip secured to the pick-up tip is partially immersed in a polymer bath such that the immersed chip is fully wetted by the polymer, the flip chip being immersed to a point such that the pick-up tip and the distal ends of the projections extend above the polymer bath, wherein the polymer bath is ultrasonically vibrated and the polymer bath has a viscosity sufficiently high such that the polymer bath is not pulled above the desired immersion point by the vacuum securing the flip chip to the pick-up tip; removing the flip chip from the polymer bath such that a coating of the polymer remains in contact with the flip chip such that the distal ends of the projections are uncoated; applying ultraviolet light or heat (e.g., IR radiation) to the coated flip chip such that an outer layer of the coating cures to form a skin-cured flip chip; releasing the skin-cured flip chip from the pick-up tip; placing the skin-cured flip chip on a substrate board to form an assembly; and applying thermal energy to the assembly, wherein the thermal energy causes the solder and the polymer to flow and also cures the polymer.
In another preferred embodiment, the invention is a method for encapsulating and underfilling a flip chip, the method comprising the steps of: providing a wafer having an upper surface, the upper surface having at least one flip chip arrayed thereon, wherein the flip chip comprises projections of conductive material on one side of the flip chip, the projections having a proximate end attached to the flip chip and a distal end opposite the proximate end; providing a pick-up tip, the tip having indentations corresponding to the projections on the flip chip, wherein small holes are defined within the indentations; positioning the tip in contact with, or close proximity to, the flip chip such that the indentations align with the projections; applying a vacuum through the indentations such that the flip chip is secured to the tip and the indentations partially cover the projections; repositioning the tip such that the flip chip secured to the tip is immersed in a polymer bath, the flip chip being immersed to a point between the proximate end of the projections and the distal end of the projections such that the distal ends of the projections are not in contact with the polymer, the polymer bath being vibrated ultrasonically to facilitate wetting of the chip around the balls, the polymer bath having a viscosity sufficiently high such that the polymer is not pulled into the vacuum; removing the flip chip from the polymer bath such that a coating of the polymer remains in contact with the flip chip such that the distal ends of the projections are uncoated; applying ultraviolet light or heat (e.g., IR radiation) to the coated flip chip such that an outer layer of the coating cures to form a skin-cured flip chip; releasing the skin-cured flip chip from the pick-up tip; placing the skin-cured flip chip on a substrate board to form an assembly; and applying thermal energy to the assembly, wherein the thermal energy causes the solder and the polymer to flow and also cures the polymer to encapsulate the coated chip.
In another preferred embodiment, the invention is a process for forming a semiconductor device, the process consisting of the steps of: providing a wafer having an upper surface, the upper surface having at least one flip chip arrayed thereon, wherein the flip chip comprises solder balls attached to a surface of the flip chip, the solder balls having a distal section and having a height above the surface of the flip chip; picking the flip chip from the upper surface of the wafer with a pick-up tip, the pick-up tip comprising indentations adapted to fit the solder balls on the flip chip, the indentations further comprising holes in fluid communication with a vacuum source; applying a vacuum through the holes in the indentations such that the flip chip is secured to the pick-up tip and the indentations at least partially cover the distal portion of the solder balls; immersing the flip chip secured to the pick-up tip in a polymer bath such that the immersed chip is fully wetted by the polymer, the flip chip being immersed to a point such that the pick-up tip and the distal ends of the solder balls, up to about one-half the height of the solder balls, extend above the polymer bath, wherein the polymer bath is ultrasonically vibrated and the polymer bath has a viscosity sufficiently high such that the polymer bath is not pulled above the desired immersion point by the vacuum securing the flip chip to the pick-up tip; removing the flip chip from the polymer bath such that a coating of the polymer remains in contact with the flip chip except for the distal ends of the solder balls; exposing the flip chip to having a coating of the polymer to ultraviolet light or heat (e.g., IR radiation) such that at least a portion of the polymer cures to form an outer skin of cured coating, thereby forming a coated chip; placing the coated chip onto a mounting surface; applying thermal energy to the coated chip on the mounting surface, wherein the thermal energy causes the solder and the polymer to reflow and also cures the polymer to encapsulate the coated chip.
In another preferred embodiment the invention is a method for encapsulating and underfilling a batch of flip chips, the method comprising the steps of: providing a multiplicity of flip chips, each flip chip having projections of conductive material on one side of the flip chip, the projections having a proximate end attached to the flip chip and a distal end opposite the proximate end; immersing the multiplicity of flip chips simultaneously in a polymer bath, wherein the polymer bath covers the flip chips and part of the projections up to a point between the proximate end of the projection and the distal end of the projection; removing the multiplicity of flip chips from the polymer bath such that a coating of polymer adheres to each flip chip and the part of the projections covered by the polymer bath to form coated flip chips having the distal ends of the projections uncoated; applying ultraviolet light or heat (e.g., IR radiation) to the multiplicity of coated flip chips such that an outer layer of each coating cures to form a skin-cured flip chip; placing the skin-cured flip chips on one or more substrate boards to form at least one assembly; heating the assembly such that: (i) the conductive material forms an electrical junction between the flip chips and the at least one substrate; (ii) the polymer from the polymer coating on the flip chip underfills and encapsulates the flip chips; and, (iii) the polymer from the coating cures.
In still another preferred embodiment the invention is a method for encapsulating and underfilling a batch of flip chips, the method comprising the steps of: providing a multiplicity of flip chip, each flip chip having projections of conductive material on one side of the flip chip, the projections having a proximate end attached to the flip chip and a distal end opposite the proximate end; providing at least one pick-up tip, the pick-up tip having indentations corresponding to the projections on the flip chips, wherein the indentations are in fluid communication with a vacuum source; positioning the at least one pick-up tip in contact with, or close proximity to, the flip chips such that the indentations align with and partially cover the projections; applying a vacuum through the indentations such that the flip chips are secured to the at least one pick-up tip; repositioning the at least one pick-up tip such that the multiplicity of flip chips secured to the pick-up tip are simultaneously immersed in a polymer bath, wherein the polymer bath covers the flip chips and part of the projections up to a point between the proximate end of the projection and the distal end of the projection; removing the flip chips from the polymer bath such that a coating of polymer adheres to each flip chip and the part of the projections covered by the polymer bath to form coated flip chips having the distal ends of the projections are uncoated; applying ultraviolet light or heat (e.g., IR radiation) to the coated flip chips such that an outer layer of the coatings cure to form a skin-cured flip chip; releasing the skin-cured flip chips from the at least one pick-up tip; placing the skin-cured flip chips on at least one substrate board to form at least one assembly; heating the at least one assembly such that: (i) the conductive material forms an electrical junction between the flip chips and the at least one substrate; (ii) the polymer from the polymer coatings on the flip chips underfills and encapsulates the flip chips; and, (iii) the polymer from the coatings cures.